Meters for metering the various forms of electrical power are well known. Utility company meters can be of three general types, namely, electromechanical based meters (output generated by a rotating disk), purely electronic component based meters (output component generated without any rotating parts) and a hybrid mechanical/electronic meter. In the hybrid meter, a so-called electronic register is coupled, usually optically, to a rotating disk. Pulses generated by the rotating disk, for example by light reflected from a spot painted on the disk, are utilized to generate an electronic output signal.
It will be appreciated that the use of electronic components in electric meters has gained considerable acceptance due to their reliability and extended ambient temperature ranges of operation. Moreover, contemporary electronic signal processing devices, such as microprocessors, have a greater accuracy potential for calculating electrical power use than prior mechanical devices. Consequently, various forms of electronic based meters have been proposed which are virtually free of any moving parts. Several meters have been proposed which include a microprocessor.
Many of the new solid-state meters also include a liquid crystal display (LCD) to convey information to individuals or equipment externally of the meter. Typically, the LCD display includes annunciators that are turned ON to indicate the presence of the different voltage phases (e.g., Phase A, Phase B, and Phase C in a polyphase meter) and turned OFF to indicated the absence of one or more of the phases. In some situations, the annunciator is flashed to indicate the absence of phase.
Providers of electricity are concerned with incorrect wiring problems, and unscrupulous individuals who tamper with meters to circumvent the metering of power consumption and payment for power usage. Therefore, meters have historically been equipped with phase voltage indications to signal the presence of voltages on individual phases. This helps detect normal phase voltage outages as well as tampering where a phase voltage is removed while the meter still appears to be operating due to the voltages on the other phases. However, older meters simply looked for the presence of a voltage, and not at the actual magnitude of the voltage. This made the assumption that if a phase voltage was removed, there would be no voltage remaining; therefore, no need to check the magnitude.
However, in metering with 2-element polyphase meters, there will typically be three voltage points that are connected, with one of the three being the reference for the other two. The two normal installations are 3-wire delta and 3-wire wye. The 3-wire delta connects to phases A and C with respect to phase B (the 3.sup.rd connection). The angle between the two voltage Va-b and Vc-b will be either 60 degrees or 300 degrees. And the two voltages will be the actual line-to-line voltage of the service. The 3-wire wye connects to phases A and C as well, but with respect to ground (the 3.sup.rd connection). The angle between the two voltages Va-g and Vc-g will either be 120 degrees or 240 degrees. And the two voltages will be the actual line-to-neutral (or ground) voltages (which is 57.7% of the line-to-line voltage).
For a 2-element meter, there have typically been two phase indicators, one for each non-reference phase. In either service type case, removal of phase A or C would generate an indication of the loss of a phase voltage since there would be no voltage on that phase with respect to the reference, and would cause one of the phase indicators to signal loss of a phase. However, if the reference voltage was lost, and the reference point was allowed to float, then the reference should float to halfway between the two remaining voltages. Now each phase to reference voltage would be 50% of the phase to phase voltage. This reduction in the voltage magnitude along with the change in angle relationship to the respective phase currents will significantly reduce the registration of the meter. However, since there is still a non-zero voltage across each phase to reference voltage, the phase indicators will still indicate presence of voltage on both phases.
Consequently, a need exists for an electronic meter that can automatically detect and indicate loss of the neutral as well as the other phase voltages due to mis-wiring or tampering. The present invention solves the aforementioned problems through the use of a novel detection technique that measures the phase angle difference between the normally connected phases (e.g. Phase A and Phase C with respect to the reference phase, either Phase B or ground depending on the service type).